Misdiagnosis of cystic fibrosis. Need for continuing follow-up and reevaluation.

A retrospective review was conducted of the charts of 271 patients with a diagnosis of cystic fibrosis (CF) who were evaluated over a 15-year period at the Johns Hopkins Hospital. Among these patients, eight were encountered in which the diagnosis of CF was made on the basis of a compatible clinical picture and at least two positive quantitative pilocarpine iontophoresis sweat tests but who were subsequently documented to have normal sweat electrolyte concentrations. Six of the eight patients had recurrent episodes of cough and wheezing without evidence of suppurative pulmonary disease. Our experience suggests that variability in sweat electrolyte concentrations may occur more commonly than is generally appreciated. In those patients who do not follow a typical course, it is crucial to repeat sweat tests, even if the initial diagnosis was based on two or more positive quantitative pilocarpine iontophoresis sweat tests performed in a CF referral center.